Method and apparatus for multi-rat transmission

ABSTRACT

A method and apparatus for mobility management, load management, sharing management and configuration update and setup in a mobile network having a first radio access technology node and a second radio access technology node, the first radio access technology node and the second radio access technology node communicating over a backhaul interface. In one aspect the method detects, at the first radio access technology node, that a handover for a user equipment to a new node is required; provides, from the first radio access technology node, handover information to the second radio access technology node over the backhaul interface; and performs the handover of the user equipment from the first radio access technology node to the new node.

FIELD OF THE DISCLOSURE

The present disclosure relates to user equipment (UE) devices supportingmultiple radio access technologies (RATs) and in particular relates tomulti-RAT carrier aggregation.

BACKGROUND

Radio access technologies have evolved through various generations toallow more functionality and higher peak data throughput rates, amongother attributes. As new RATs are deployed, the use of legacy RATs thatdo not have the same functionality as the new RATS will likely begin todecline. The decline in traffic may create white space in frequencybands allocated to the legacy RAT, where the white space couldpotentially be used by the new RATs in cases where the new RATs may nothave enough available bandwidth when initially deployed.

Currently, when a base station is overloaded and can no longer supportthe demand for initial bandwidth, the serving base station may forcesome UEs to handover to other neighboring base stations. The neighboringbase stations may be selected based on the capability of a UE to receivethe signal from the neighboring cell with an acceptable quality.Neighbor base stations may operate the same RAT or may be of differentRATs.

Within current Third Generation Partnership Project (3GPP)specifications, technologies such as Long Term Evolution (LTE) have abackhaul interface that may be defined between neighboring nodes.However in this case, the neighboring nodes belong to the same RAT.There is no backhaul interface currently defined in 3GPP for neighboringnodes of different RATs.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be better understood with reference to thedrawings, in which:

FIG. 1 is a block diagram illustrating one example architecture forcarrier aggregation at a multi-RAT user equipment;

FIG. 2 is a flow diagram illustrating the establishment of a connectionbetween a plurality of RATs and a UE;

FIG. 3 is an architecture diagram of network nodes and connections for aplurality of radio access technologies;

FIG. 4 is a block diagram illustrating a protocol stack for elementswithin an E-UTRAN network;

FIG. 5 is a block diagram illustrating a protocol stack for elementswithin an UTRAN network;

FIG. 6 is a protocol stack for a user plane for a backhaul interfacebetween a first radio access technology node and a second radio accesstechnology node;

FIG. 7 is a protocol stack for a control plane for a backhaul interfacebetween a first radio access technology node and a second radio accesstechnology node;

FIG. 8 is a flow diagram for signaling in a multi-RAT network;

FIG. 9 is a protocol stack showing signaling between elements within amulti-RAT network;

FIG. 10 is a process diagram showing the modifications to a packet beingcommunicated over a multi-RAT network at the PDCP layer;

FIG. 11 is a block diagram showing a multi-RAT interface at the RLClayer;

FIG. 12 is a block diagram showing a multi-RAT interface at the MAClayer;

FIG. 13 is a block diagram showing a protocol stack adding a newmulti-RAT protocol layer;

FIG. 14 is a flow diagram showing handover at a primary RAT;

FIG. 15 is a flow diagram showing handover at a secondary RAT;

FIG. 16 is a flow diagram showing handover at a primary and secondaryRAT;

FIG. 17 is a flow diagram showing handover from the primary RAT to thesecondary RAT;

FIG. 18 is a simplified block diagram of an example network element; and

FIG. 19 is a block diagram of an example user equipment.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure provides a method for mobility management in amobile network having a first radio access technology node and a secondradio access technology node, the first radio access technology node andthe second radio access technology node communicating over a backhaulinterface, the method comprising: detecting, by the first radio accesstechnology node, that a handover for a user equipment to a new node isrequired; providing, by the first radio access technology node, handoverinformation to the second radio access technology node over the backhaulinterface; and performing, by the first radio access technology node,the handover of the user equipment to the new node.

In one embodiment, the first radio access technology node routes thedata packets to the second radio access technology node during thehandover of the first radio access technology node. In one embodimentthe performing the handover comprises: sending a handover requestmessage, which includes context information of the user equipment, tothe new node; sending a handover command to the user equipment;forwarding data to the new node; receiving a handover complete messagefrom the new node; and detaching the backhaul interface with the secondradio access technology node.

In one embodiment the new node establishes a backhaul interface with thesecond radio access technology node. In one embodiment the establishingis based on context information received from the first radio accesstechnology node. In one embodiment the second radio access technologynode establishes the backhaul interface to the new node on receivinghandover information from the first radio access technology node.

In one embodiment the new node is of the same radio access technology asthe first radio access technology node. In one embodiment the firstradio access technology node includes an interface to a core network forthe user equipment. In one embodiment the second radio access technologynode includes a tunnel to a core network for the user equipment. In oneembodiment the performing the handover does not change the tunnel to thecore network.

In one embodiment, the method includes after performing the handover:detecting, at the new node, that a handover from the second radio accesstechnology node is required; establishing, between the new node and atarget second radio access technology node, a backhaul interface; andproviding, from the new node to the user equipment, information forsynchronization with the target second radio access technology node.

In one embodiment, the establishing includes determining whether thetarget second radio access technology node can support the userequipment. In one embodiment, the determining includes receivingcapability information from a measurement report from the user equipmentof whether the target second radio access technology node supportsmulti-radio access technology carrier aggregation. In one embodiment thedetermining includes receiving capacity information for the targetsecond radio access technology node over the backhaul interface. In oneembodiment the target second radio access technology node does notestablish a tunnel with a core network.

The present disclosure further provides a first radio access technologynode configured for mobility management in a mobile network having thefirst radio access technology node and a second radio access technologynode, the first radio access technology node and the second radio accesstechnology node communicating over a backhaul interface, the first radioaccess technology node comprising: a processor; and a communicationssubsystem, wherein the processor and communications subsystem areconfigured to: detect that a handover for a user equipment to a new nodeis required; provide handover information to the second radio accesstechnology node over the backhaul interface; and perform the handover ofthe user equipment to the new node.

In one embodiment, the processor and communications subsystem arefurther configured to route the data packets to the second radio accesstechnology node during the handover of the first radio access technologynode. In one embodiment the processor and communications subsystem arefurther configured to perform the handover by: sending a handoverrequest message, which includes context information of the userequipment, to the new node; sending a handover command to the userequipment; forwarding data to the new node; receiving a handovercomplete message from the new node; and detaching the backhaul interfacewith the second radio access technology node.

In one embodiment the new node establishes a backhaul interface with thesecond radio access technology node. In one embodiment the establishingis based on context information received from the first radio accesstechnology node. In one embodiment, the second radio access technologynode establishes the backhaul interface to the new node on receivinghandover information from the first radio access technology node. In oneembodiment the new node is of the same radio access technology as thefirst radio access technology node.

In one embodiment the first radio access technology node includes aninterface to a core network for the user equipment. In one embodiment,the second radio access technology node includes a tunnel to a corenetwork for the user equipment. In one embodiment the performing thehandover does not change the tunnel to the core network.

The present disclosure further provides a method for mobility managementin a mobile network having a first radio access technology node and asecond radio access technology node, the first radio access technologynode and the second radio access technology node communicating over abackhaul interface, the method comprising: detecting, by the first radioaccess technology node, that a handover for a user equipment isrequired; providing, by the first radio access technology node, ahandover request to the second radio access technology node over thebackhaul interface; and sending, by the first radio access technologynode, a handover command to the user equipment.

In one embodiment the method further comprises: receiving an end markerfrom a serving gateway; forwarding the end marker to the second radioaccess technology node; and detaching the backhaul interface between thefirst radio access technology node and the second radio accesstechnology node, wherein the second radio access technology nodeperforms a path switch with the serving gateway after receiving thehandover request. In one embodiment the method further comprisesreceiving a UE context release message from the second radio accesstechnology node.

The present disclosure further provides a first radio access technologynode configured for mobility management in a mobile network having thefirst radio access technology node and a second radio access technologynode, the first radio access technology node and the second radio accesstechnology node communicating over a backhaul interface, the first radioaccess technology node comprising: a processor; and a communicationssubsystem, wherein the processor and communications subsystem areconfigured to: detect, at the first radio access technology node, that ahandover for a user equipment is required; provide, from the first radioaccess technology node, a handover request to the second radio accesstechnology node over the backhaul interface; and send a handover commandto the user equipment from the first radio access technology node.

In one embodiment the processor and communications subsystem are furtherconfigured to: receive an end marker from a serving gateway; forward theend marker to the second radio access technology node; and detach thebackhaul interface between the first radio access technology node andthe second radio access technology node, wherein the second radio accesstechnology node performs a path switch with the serving gateway afterreceiving the handover request. In one embodiment the processor andcommunications subsystem are further configured to receive a UE contextrelease message from the second radio access technology node.

The present disclosure further provides a method for establishingcarrier aggregation between a first node having a first radio accesstechnology and a second node having a second radio access technology,the method comprising: determining, by the first node, that a userequipment is capable of multi-radio access technology carrieraggregation; determining, by the first node, that the second node isavailable for the user equipment; establishing, by the first node, abackhaul interface with the second node; forwarding, by the first node,data regarding the user equipment to the second node; and forwarding, bythe first node, a connection request to the user equipment to connect tothe second node.

In one embodiment the method further comprises detecting that a ratio ofneeded bandwidth to available radio resources exceeds a threshold. Inone embodiment the determining that the second node is availablecomprises: requesting a measurement report from the user equipment; andreceiving the measurement report. In one embodiment the connectionrequest includes connection information for the second node.

In one embodiment the connection information includes a random accesspreamble. In one embodiment the connection information includessynchronization information for the second node. In one embodiment, oncethe user equipment is connected to the second node, identical data istransmitted simultaneously to both the first node and the second node.In one embodiment, once the user equipment is connected to the secondnode, different data is transmitted to each of the first node and thesecond node during a transmission time interval.

In one embodiment the first node further sends an indication to the userequipment indicating whether communication with the second node issymmetrical. In one embodiment the first node and the second node aretime synchronized.

The present disclosure further provides a first node having a firstradio access technology configured for carrier aggregation with a secondnode having a second radio access technology, the first node comprising:a processor; and a communications subsystem, wherein the processor andcommunications subsystem are configured to: determine that a userequipment is capable of multi-radio access technology carrieraggregation; determine that the second node is available for the userequipment; establish a backhaul interface between the first node and thesecond node; forward data regarding the user equipment to the secondnode; and forward a connection request to the user equipment to connectto the second node.

In one embodiment the processor and communications subsystem are furtherconfigured to detect that a ratio of needed bandwidth to available radioresources exceeds a threshold. In one embodiment the processor andcommunications subsystem are configured to determine that the secondnode is available by: requesting a measurement report from the userequipment; and receiving the measurement report. In one embodiment theconnection request includes connection information for the second node.

In one embodiment the connection information includes a random accesspreamble. In one embodiment the connection information includessynchronization information for the second node. In one embodiment, oncethe user equipment is connected to the second node, identical data istransmitted simultaneously to both the first node and the second node.In one embodiment, once the user equipment is connected to the secondnode, different data is transmitted to each of the first node and thesecond node during a transmission time interval.

In one embodiment, the processor and communications subsystem arefurther configured to send an indication to the user equipmentindicating whether communication with the second node is symmetrical. Inone embodiment the first node and the second node are time synchronized.

The present disclosure further provides a method at a user equipmentoperating in a mobile network having a first node with a first radioaccess technology and a second node with a second radio accesstechnology, the method comprising: receiving, from the first node arequest to perform an inter-radio access technology neighbor cellmeasurement; performing the inter-radio access technology neighbor cellmeasurement; and providing a report to the first network node, thereport including an indication of whether a neighbor cell supportsinter-radio access technology carrier aggregation.

In one embodiment the indication is a single bit. In one embodiment, themethod further comprises receiving a request to connect to the secondnode. In one embodiment the request includes information to assist theuser equipment to connect to the second node. In one embodiment theinformation includes a random access preamble to be used by the userequipment for the connection. In one embodiment the information includessynchronization information for the second node. In one embodiment themethod further comprises establishing a connection with the second node,the establishing including sending a user equipment identifier for theuser equipment on the first node to the second node.

The present disclosure further provides a user equipment operating in amobile network having a first node with a first radio access technologyand a second node with a second radio access technology, the userequipment comprising: a processor; and a communications subsystem,wherein the processor and communications subsystem are configured to:receive, from the first node a request to perform an inter-radio accesstechnology neighbor cell measurement; perform the inter-radio accesstechnology neighbor cell measurement; and provide a report to the firstnetwork node, the report including an indication of whether a neighborcell supports inter-radio access technology carrier aggregation.

In one embodiment the indication is a single bit. In one embodiment theprocessor and communications subsystem are further configured to receivea request to connect to the second node. In one embodiment the requestincludes information to assist the user equipment to connect to thesecond node. In one embodiment the information includes a random accesspreamble to be used by the user equipment for the connection. In oneembodiment the information includes synchronization information for thesecond node. In one embodiment the processor and communicationssubsystem are further configured to establish a connection with thesecond node, the establishing including sending a user equipmentidentifier for the user equipment on the first node to the second node.

The present disclosure further provides a method at a first node of afirst radio access technology for communicating data received from asecond node having a second radio access technology to a user equipment,the method comprising: receiving the data, the data being a protocollayer packet of the second radio access technology; adding a sequencenumber to the protocol layer packet; adding a multi-radio accesstechnology header to the protocol layer packet; and forwarding thepacket to the user equipment.

In one embodiment the adding the multi-radio access technology headerskips other protocol layer functionality for a protocol layer. In oneembodiment the protocol layer packet is a packet data convergenceprotocol layer packet. In one embodiment the method further comprisesadding a protocol layer header after the adding the multi-radio accesstechnology header. In one embodiment the receiving is over a multi-radioaccess technology backhaul interface.

The present disclosure further provides a first node of a first radioaccess technology for communicating data received from a second nodehaving a second radio access technology to a user equipment, the firstnode comprising: a processor; and a communications subsystem, whereinthe processor and communications subsystem are configured to: receivethe data, the data being a protocol layer packet of the second radioaccess technology; add a sequence number to the protocol layer packet;add a multi-radio access technology header to the protocol layer packet;and forward the packet to the user equipment.

In one embodiment the processor and communications subsystem are furtherconfigured skip other protocol layer functionality for a protocol layer.In one embodiment the protocol layer packet is a packet data convergenceprotocol layer packet. In one embodiment the processor andcommunications subsystem are further configured to add a protocol layerheader after the adding the multi-radio access technology header. In oneembodiment the processor and communications subsystem are configured toreceive is over a multi-radio access technology backhaul interface.

The present disclosure further provides a method at a user equipmentcommunicating with both a first node having a first radio accesstechnology and a second node having a second radio access technology,the second node having a tunnel to a core network, the methodcomprising: receiving a protocol layer packet from the first node at theuser equipment; and at a first radio access technology protocol layercorresponding to the protocol layer packet: removing a multi-radioaccess technology header; ordering the packet; and forwarding the packetto a second radio access technology protocol layer corresponding to thefirst radio access technology protocol layer.

In one embodiment, the first radio access technology protocol layer is apacket data convergence protocol (PDCP) layer. In one embodiment theremoving the multi-radio access technology header further comprisingskipping other PDCP layer functionality. In one embodiment the methodfurther comprises removing a PDCP header before removing the multi-radioaccess technology header.

In one embodiment the first radio access technology protocol layer is aradio link control (RLC) layer. In one embodiment, the method furthercomprises receiving an RLC protocol data unit (PDU) segment size for atransmission opportunity. In one embodiment the removing the multi-radioaccess technology header further comprising skipping other RLC layerfunctionality.

In one embodiment the first radio access technology protocol layer is amedium access control (MAC) layer. In one embodiment, after the removingthe multi-radio access technology header, the packet is treated as a MACservice data unit. In one embodiment the method further comprisesreceiving an MAC protocol data unit (PDU) segment size for atransmission opportunity.

In one embodiment the first radio access technology protocol layer is aninternet protocol (IP) layer. In one embodiment a further multi-radioaccess technology protocol layer is used to handle radio accesstechnology selection.

In one embodiment the first radio access technology protocol layer is amulti-radio access technology protocol layer. In one embodiment themethod further comprises combining identical packets received from thefirst node and the second node.

The present disclosure further provides a user equipment communicatingwith both a first node having a first radio access technology and asecond node having a second radio access technology, the second nodehaving a tunnel to a core network, the user equipment comprising: aprocessor; and a communications subsystem; wherein the processor andcommunications subsystem are configured to: receive a protocol layerpacket from the first node at the user equipment; and at a first radioaccess technology protocol layer corresponding to the protocol layerpacket: remove a multi-radio access technology header; order the packet;and forward the packet to a second radio access technology protocollayer corresponding to the first radio access technology protocol layer.

In one embodiment the first radio access technology protocol layer is apacket data convergence protocol (PDCP) layer. In one embodimentremoving the multi-radio access technology header further comprisesskipping other PDCP layer functionality. In one embodiment the processorand communications subsystem are further configured to remove a PDCPheader before removing the multi-radio access technology header.

In one embodiment the first radio access technology protocol layer is aradio link control (RLC) layer. In one embodiment the processor andcommunications subsystem are further configured to receive an RLCprotocol data unit (PDU) segment size for a transmission opportunity. Inone embodiment the removing the multi-radio access technology headerfurther comprises skipping other RLC layer functionality.

In one embodiment the first radio access technology protocol layer is amedium access control (MAC) layer. In one embodiment, after the removingthe multi-radio access technology header, the packet is treated as a MACservice data unit. In one embodiment the processor and communicationssubsystem are further configured to receive a MAC protocol data unit(PDU) segment size for a transmission opportunity.

In one embodiment the first radio access technology protocol layer is aninternet protocol (IP) layer. In one embodiment a further multi-radioaccess technology protocol layer is used to handle radio accesstechnology selection.

In one embodiment the first radio access technology protocol layer is amulti-radio access technology protocol layer. In one embodiment theprocessor and communications subsystem are further configured to combineidentical packets received from the first node and the second node.

In order to allow UE to simultaneously transmit and receive packets frommultiple RATs, the present disclosure provides for a new multi-RATbackhaul interface. The new backhaul may be used to divert packets toanother node that is operating in a different RAT than the serving node.The multi-RAT backhaul may be used to enable multi-RAT carrieraggregation (CA).

Carrier aggregation allows the expansion of effective bandwidthdelivered to a mobile device through concurrent utilization of radioresources across multiple frequency carriers. The multiple carriers arethen aggregated to form a larger overall transmission bandwidth. In 3GPPHigh Speed Packet Access (HSPA), carrier aggregation was introduced inRelease 8. Currently, up to 8 high speed downlink packet access (HSDPA)carriers may be aggregated in Release 11.

Similarly, in 3GPP Long Term Evolution, carrier aggregation for up to 5LTE carriers has been introduced in Release 10. Also, downlink dual bandoperation was introduced in Release 9 for HSPA dual carrier operationand for LTE carrier aggregation in Release 10.

Since most operators need to operate both HSPA and LTE technologies inparallel and there is limited spectrum available, the potential existsfor a HSPA and/or LTE carrier aggregation which may not be fullyexploited. Further, the re-farming of existing spectrum using HSPA forLTE may lower the data rates to HSPA-only users. Since HSPA datacoverage may be maintained for use by existing HSPA devices, migratingthe HSPA spectrum to LTE may not be possible. The aggregation of LTE andHSPA carriers allows the HSPA capacity to be made available to the LTEdevices, while serving the existing HSPA devices.

While the present disclosure discusses HSPA and LTE carrier aggregation,the present disclosure is not limited to those two RATs. In particular,any two RATs may be combined in accordance with the embodiments of thepresent disclosure. Examples of other RATs include Wi-Fi, Wi-MAX, secondgeneration technologies, third generation technologies, among others.The use of any two RATs having a wired backhaul link and communicationchannels with each other may allow for the benefits of the presentdisclosure to be achieved.

The aggregation of HSDPA with LTE Downlink carriers for multi-RATcapable devices may improve spectrum utilization, provide dynamic loadbalancing between the two technologies to handle the short term loadvariations that result from bursty data traffic, provide a combined peakdata rate and improve cell edge user data rates and average user datarates.

For example, an operator that has 15 MHz available for both LTE and HSPAmay, using multi-RAT carrier aggregation, be able to offer aggregatedpeak data rates of the two systems rather than the peak data rate ofonly one of the systems. Although, a higher peak rate may be offered ifboth bands were operating the same RAT, this may not be possible sincelegacy and new UEs must both be served.

As indicated above, in wireless standards such as 3GPP LTE and WiMAX,multiple carriers of the same RAT may be aggregated to both the uplink(UL) and the downlink (DL). By introducing a multi-RAT backhaulinterface between different RATs, multi-RAT carrier aggregation may beenabled between different RATs at different access points or basestations (BS). In multi-RAT carrier aggregation (CA), carriers are usedby different nodes from different networks and may be operating usingdifferent RATs may be allocated to the UE for one or both of downlink oruplink transmission. In this case, a UE may be able to transmit orreceive one or more service flows on multiple RATs in order to improveits quality of service (QoS). If the evolved Node B (eNB) detects thatthe available bandwidth is not sufficient to provide all servicesrequired by a UE, then the eNB may configure a multi-RAT backhaul to aneighboring node that is operating a different RAT to enable multi-RATcarrier aggregation. The serving eNB of the UE may make this decisionbased on a UE's capability to handle multi-RAT carrier aggregation andthe available resources at the other RAT.

The multi-RAT backhaul interface may be at the medium access control(MAC) layer, the radio link control (RLC) layer, the packet dataconvergence protocol (PDCP) layer or at the internet protocol (IP)layer. In each case, a RAT selection procedure is provided below whichdetermines the best RAT on which to send the packets.

Reference is now made to FIG. 1. In multi-RAT carrier aggregation, oneRAT may be the primary RAT, which is used for initial access. Forexample, a multi-RAT capable user equipment (UE) may perform initialaccess on an LTE network. The LTE eNB may then instruct the UE toestablish a connection to an HSPA NodeB. In this case, data can beforwarded by the LTE eNB to the HSPA NodeB or radio network control(RNC) rather than establishing another path from the core network to theNodeB.

In particular, in FIG. 1, a multi-RAT UE 110 has a communicationssubsystem 112 capable of supporting LTE, as well as a communicationssubsystem 114 capable of supporting HSPA.

Initially, UE 110 is connected through eNB 120 over the LTEcommunication subsystem 112 to a core network 130. The eNB 120 thendecides that multi-RAT carrier aggregation would be beneficial and usesa backhaul communication 122 to communicate with a NodeB 140 of an HSPAnetwork.

RNC 142 communicates with NodeB 140, as shown in FIG. 1.

NodeB 140 and UE 110 then establish communication over the HSPAcommunication subsystem 114.

However, as seen in FIG. 1, only a single connection 150 exists betweencore network 130 and eNB 120. Thus, communications that are directedthrough the HSPA network and in particular through NodeB 140 are thendirected over the backhaul interface 122 to eNB 120 before beingforwarded to core network 130. This may be accomplished, as described inmore detailed below, by encapsulating packets with a multi-RAT headerand then removing the multi-RAT header at the eNB prior to forwardingthe data packet to a core network.

As used herein, a primary RAT is defined as the RAT that has theconnection to the core network and the secondary RAT is defined as theRAT that communicates through the primary RAT in order to communicatewith the core network 130.

The network node on the secondary RAT may be co-located with the networknode of the primary RAT or it may be at a different site in accordancewith various embodiments of the present disclosure.

The use of a multi-RAT interface transmission procedure provides formobility management, load management, sharing management andconfiguration updates and setup.

In particular, for mobility management, the multi-RAT interface providesuser data and control signals transferred between multi-RAT networks.Mobility management allows for the primary RAT to move responsibility ofa certain UE to a secondary RAT and it also allows a secondary RAT tomove responsibility of a certain UE to the primary RAT.

With regard to load management, the load management function indicatesresource status, overload and traffic load on multi-RAT interfaces. Asharing request may be sent from the primary or secondary RAT to thesecondary or primary RAT to control the load balancing of the primary orsecondary RAT when heavily loaded. The request is sent to quicklyresolve loading problems using multi-RAT interfaces.

With regard to sharing management, a sharing management functionprovides for error recovery procedures to recover from irregular,uncertain or incorrect operation on a multi-RAT interface. The sharingmanagement also allows for resetting of the link by booting-up frominitialization or by resetting all of the functions.

With regard to configuration updates and setup, configuration update andsetup functionality provides any update of the link on a multi-RATinterface.

The above four functions are shown below with regard to Table 1.

TABLE 1 Major functions and operations for a multi-RAT interface MainFunctions Sub-operation Mobility Management Handover Status informationUE context release Load Management Load indication Load sharing Resourcestatus Sharing Management Error reporting System reset Configurationupdate and setup Multi-RAT link setup Update

As seen in Table 1, the main functions include sub-operations. Thus,mobility management includes handovers, status information and UEcontext release. Load management includes load indication and loadsharing and resource status. Sharing management includes error reportingand system resets. Configuration updates and setups includes multi-RATlink setups and updates.

Each of the sub-operations of Table 1 above are shown in more detailbelow with regard to Table 2.

TABLE 2 Contents and procedures for sub-operations Sub-operationBehaviour Handover Resource preparation and link establishment forexpected handover operation. (e.g. handover request, handover response,handover cancel, handover failure etc.) Status Information Transfer ofstatus of UL/DL PDCP SN (Sequence number) and HFN (Hyper Frame Number)receiver status UE Context Release of radio and control plane resourcesRelease and profile for the handed over UE Load Indication Exchange ofLoad information of neighbour RATs Load Sharing A certain RAT requeststhe sharing to another RAT system to balance its load status ResourceStatus Neighbour RATs request the reporting of the load measurement andavailable resources for handover and similar operation Error ReportingNeighbour RATs transmit the indication to each other when an erroroccurred System Reset When a malfunction occurs or the system is down, asystem reset procedure will be automatically or manually initiatedMulti-RAT Link After resetting of the link, Multi-RAT link will be Setupsetup again Update If there are any updates due to changing of theenvironment or network configuration, updates among neighbor RATs willbe performed

As seen from Table 2 above, the sub-operations include variousbehaviors. For example, handover has the behavior of resourcepreparation and link establishment for expected handover operations, andmay include the handover request, handover response, handover cancel,handover failure, among others.

The behaviors of Table 2 may be facilitated utilizing various messages.Reference is now made to Table 3, which shows various messages used toinitiate some actions and related responses for the operations. Thenaming of the messages is meant as an example only and may, inimplementation, be different. However, the purpose of the message wouldbe for use by multi-RAT networks.

TABLE 3 Messages for a multi-RAT interface Sub-operation MessagesHandover HANDOVER REQUEST HANDOVER RESPONSE (SUCCESS and FAIL) HANDOVERCANCEL Status STATUS REQUEST Information STATUS RESPONSE UE ContextCONTEXT REQUEST CONTEXT RESPONSE CONTEXT RELEASE Load Indication LOADINFORMATION REQUEST LOAD INFORMATION RESPONSE Load Sharing LOAD SHAREREQUEST LOAD SHARE RESPONSE (SUCCESS and FAIL) Resource RESOURCE STATUSREQUEST Status RESOURCE STATUS RESPONSE Error Reporting ERROR INDICATIONSystem Reset SYSTEM RESET REQUEST SYSTEM RESET RESPONSE (SUCCESS andFAIL) Multi-RAT link LINK SETUP REQUEST setup LINK SETUP RESPONSE(SUCCESS and FAIL) Update UPDATE REQUEST

Thus, in accordance with Table 3, a handover may include a handoverrequest, a handover response which indicates success or failure, or ahandover cancel message, for example.

Reference is now made to FIG. 2, which illustrates a multi-RAT procedurein which an LTE is the primary RAT and HSPA is the secondary RAT.However this is not limiting and is only meant as an example.

In particular, UE 210 communicates with an LTE eNB 212 as well as anHSPA NodeB 214. At arrow 220, UE 210 performs initial access on the LTEcarrier and establishes a data service on the downlink and/or theuplink. The UE indicates in the message of arrow 220 that it is capableof multi-RAT carrier aggregation when a radio resource control (RRC)connection is established.

The data connection is established and is shown by arrow 222.

At some point, the serving eNB 212 detects that the ratio of the sum ofrequired bandwidth to the available radio resources becomes higher thana predetermined threshold. This may be a result of downlink traffic forUE 210 or may be as a result of a message such as that shown by arrow230 requesting additional bandwidth between UE 210 and LTE eNB 212. Theserving eNB 212 may then request an inter-RAT neighbor cell measurementreport from UEs who are capable of multi-RAT carrier aggregation. Themeasurement request is sent to UEs, including UE 210, as shown by arrow232.

In response to receiving a measurement request at arrow 232, UE 210 thensends a measurement report, as shown by arrow 234, back to LTE eNB 212.The measurement report at arrow 234 may contain an indicator if themeasured node is capable of multi-RAT carrier aggregation.

From the reported measurements, eNB 212 can decide to communicate with aneighbor network node such as HSPA NodeB 214 for assistance if the UE isdetermined to have acceptable reception with respect to that node. AnX2-like interface may be established between the eNB and the NodeB/RNC,as shown by arrow 240.

If the NodeB 214 has enough bandwidth, it may acknowledge the eNBrequest. The NodeB may indicate available bandwidth if it does not havefull bandwidth available as requested by the eNB. Thus, communicationsare bi-directional, as shown by arrow 240.

Based on availability of the network neighboring node, eNB 212 mayinstruct UE 210 to establish communication with the neighboring node, asshown by arrow 250. The message at arrow 250 may include information tothe UE to allow transmission to be enabled on the NodeB and can, forexample, include downlink synchronization with HSPA NodeB 214, shown byblock 254

Further, LTE eNB 212 may forward data related to UE 210 to HSPA NodeB214, as shown by arrow 252.

UE 210 may send an acknowledgement to eNB 212 and initiate a connectionto NodeB 214 to enable the service. Connection establishment is shown byarrow 260 and may be a simplified connection establishment proceduresince certain connection parameters do not need to be established. Forexample, encryption keys to communicate with a core network do not needto be exchanged for connection establishment to a secondary RAT in someembodiments. Further, the request shown by arrow 250 may includeinformation such as dedicated preambles for random access channel (RACH)establishment to simplify connection establishment and remove contentionbased connection establishment.

Subsequently, downlink data may be received at UE 210 from one or bothof eNB 212 or NodeB 214, as shown by arrows 270 and 272. Further, uplinkacknowledgements or negative acknowledgements may be provided, as shownby arrows 280 and 282 between the UE and the eNB 212 and NodeB 214respectively.

For uplink transmission, the UE may send the uplink request to one ofthe RATS or both. If provided with an uplink grant on both RATs, the UEmay send either the same packet to improve error rates and packet delay,or different packets to improve throughput, dependent on theimplementation requirements.

In another embodiment, the multi-RAT transmission procedure may be usedby mobile relay nodes to send and/or receive packets on the relaybackhaul. In this case, multiple radio bearers for different UEs can beoffloaded onto a secondary RAT as needed. The mobile relay node behavessimilarly to a UE in the multi-RAT transmission procedure.

In one embodiment, transmission over different RATs may allow identicaldata to be transmitted simultaneously to facilitate handover. Inparticular, the simultaneous transmission may be used to enable a ‘makebefore break’ handover which may prevent inter-RAT handover failuresthat can occur quite often, especially in the small cells or hotspotswithin heterogeneous network environments. This may be from eitherhanding over too early, for example from a universal mobile terrestrialservice (UMTS) to a small cell LTE, or a “hand over too late”, forexample from a small LTE to a UMTS.

An additional bit may be used to indicate simultaneous identical(duplicate) or different data transmissions over different RATs. Thus,the bit may indicate that the data between the two RATs is identical forone value, and conversely if the bit is toggled the bit may indicatethat the transmissions are different between the RATs. The bit may beused for both over-the-air interfaces as well as along a backhaul, andcan be used to indicate which type of transmission is used.

If the bit is used for PDCP, the bit can be used to select or combinethe same packet data control protocol (PDCP) sequence number (SN) beforehandover.

In establishing the multi-RAT backhaul, the primary RAT may send arequest to a secondary RAT to handle a service flow for a specified UE.If the secondary RAT has enough trust in the primary RAT, theauthentication that is done by the primary RAT may be accepted by thesecondary RAT. The message from the primary RAT includes an identifierfor the UE in the request so that the secondary RAT may authenticate theUE when it initiates the connection establishment procedure with thesecondary RAT. Multi-RAT backhaul requests may include the amount ofresources needed for assisting transmission to the UE.

Further, on receiving a multi-RAT backhaul request for a specified UEfrom a primary RAT, the secondary RAT may send an acknowledgementmessage to the primary RAT. This acknowledgement message may include theamount of resources that can be allocated for the specified UE, whichmay be different than that requested. Other information that may also beincluded in the acknowledgement message to simplify connectionestablishment procedures for the UE may also be provided. For example,the response may include the random access preamble to be used by the UEin order to avoid a contention based random access procedure.

On receiving the acknowledgement message from the secondary RAT, theprimary RAT may instruct the UE to enable the secondary RAT. Thisrequest to the UE may include information sent by the secondary RAT tothe primary RAT for assisting the connection establishment procedure,such as the random access preamble and/or the resources to use forrandom access.

During the connection establishment procedure with the secondary RAT,the UE synchronizes with the secondary RAT network node using asynchronization procedure of the secondary RAT. This procedure mayinvolve sending a random access preamble as instructed by the primaryRAT. The UE may be assigned a dedicated random access preamble anddedicated resources to send the preamble. Although this procedure may besimilar to the procedure used by the secondary RAT for its own UEs, in amulti-RAT transmission case the UE may also send its user equipmentidentifier (UE ID) on the primary RAT in order for the secondary RAT toauthenticate the UE.

The random access response message may include the timing offsets andthe UE ID to be used on the secondary RAT. Other information such as theallocation of dedicated control channels may also be included. If the UEis configured for multi-RAT carrier aggregation on both the downlink andthe uplink, then uplink feedback channels for a channel qualityindicator (CQI) and acknowledgement or negative acknowledgement(ACK/NACK) feedback may be configured on the secondary RAT.

Alternatively, the UE may send some or all of its signalling message forthe secondary RAT over the primary RAT. For example, the UE's bufferstatus report may be sent to the primary RAT and the information can beprovided to the secondary RAT by the primary RAT using a multi-RATbackhaul interface. The UE may also send live feedback and hybridacknowledgement repeat request (HARQ) ACK/NACK for the secondary RAT onthe primary RAT. This may involve the UE saving power by transmittingdata on only one RAT at a time, even though it may receive data on bothRATs simultaneously. In some embodiments, the UE may be configured totransmit on the both the primary and the second RAT or in other cases onthe primary RAT only, based on the UE's capabilities.

In one embodiment, an indication within UE configuration information mayinclude whether or not multi-RAT transmission is symmetrical in theuplink and downlink, or not. If not, the configuration information mayinclude whether the uplink transmissions are sent on the primary or thesecondary RAT.

When the UE sends the UL HARQ ACK/NACK for the secondary RAT on theprimary RAT, the HARQ protocol of the primary RAT may be used. In thiscase, the multi-RAT configuration procedure may contain a mapping formulti-carrier HARQ feedback. For example, if a UE is allocated two DLcarriers, one for the primary RAT and the other for the secondary RAT,and only one UL carrier on the primary RAT then the HARQ feedback forboth RATs may be sent on the UL of the primary RAT. The carrier indexfor the HARQ feedback will indicate whether or not the HARQ ACK/NACK isforwarded to the secondary RAT over the multi-RAT backhaul interface.

In some embodiments, if the UE does not complete the connection with thesecondary RAT within a specified time, the secondary RAT may assign theavailable resources to other UEs. The specified time may be negotiated,in some embodiments, between the primary and the secondary RAT.

Once the UE successfully connects with the network node of the secondaryRAT, data that is forwarded by the primary RAT to the secondary RAT canbe sent to the UE on the secondary RAT.

In order to simplify the multi-RAT transmission processes, the primaryRAT and the secondary RAT may be time synchronized. The synchronizationmay be at the transmission time interval (TTI) boundary or at the radioframe boundary. If the UE is configured to only aggregate the multi-RATcarriers on the downlink, then the UE may send ACK/NACK feedback to theprimary RAT. In this case, time synchronization between the primary andthe secondary RATs may simplify the ACK/NACK feedback process.

Multi-RAT Backhaul

Reference is now made to FIG. 3, which shows an architectural diagramfor a multi-RAT backhaul in accordance with one embodiment of thepresent disclosure.

In the embodiment of FIG. 3, an exemplary architecture is shown havingan LTE network as well as a HSPA network. In particular, in theembodiment of FIG. 3, 3GPP access is shown with regard to referencenumeral 310. Within the 3GPP access, a first eNB 320 and a second eNB322 communicate through an X2 interface 324.

eNB 320 communicates with a serving gateway (SGW) 330 using an S1-Uinterface 332. Similarly, eNB 322 could also communicate with SGW 330,although this is not shown for simplicity in the embodiment of FIG. 3.

The eNB 320 also communicates with a mobility management entity (MME)340 over an S1-MME interface 342 and MME 340 communicates with SGW 330over an S11 interface 344.

In the embodiment of FIG. 3, a NodeB/RNC 350 is the contact point forthe HSPA network. In accordance with the embodiment of presentdisclosure, eNB 320 communicates with either the NodeB or the RNC 350over a multi-RAT X2 interface 352. The multi-RAT X2 interface 352 isdescribed below in more detail.

The NodeB/RNC 350 communicates with the SGW 330 over an S4 interface354. NodeB/RNC 350 communicate with the MME 340 through an S3 interface356.

SGW 330 further communicates with a packet data network gateway 360 overan S5 or S8 interface 362.

The multi-RAT interface 352 is introduced between neighboring universalterrestrial radio access network (UTRAN) and evolved UTRAN (E-UTRAN)nodes. The multi-RAT X2 interface is similar to the X2 interface betweenneighboring eNBs in E-UTRAN. However, since the NodeB UTRAN terminatesat layer 2, multi-RAT X2 interface is between the eNB and the RNC of theNodeB if the multi-RAT X2 interface is at the RLC layer or the PDCPlayer. If the interface is at the MAC layer then the backhaul is betweenthe eNB and the NodeB. These protocol layers are shown below withregards to FIGS. 4 and 5.

Reference is now made to FIG. 4, which shows a protocol stack for anE-UTRAN. In particular, each element within the network has a number ofprotocols. UE 410 includes a layer 1 (L1) 412, a MAC layer 414, a radiolink control (RLC) layer 416, a PDCP layer 418, an internet protocol(IP) layer 420 and an application layer 422.

Typically, communications between elements of the network occur at thesame level in the protocol stack. Thus, eNB 430 includes L1 432 forcommunicating with L1 412, a MAC layer 434 for communicating with MAClayer 414, an RLC layer 436 for communicating with RLC layer 416, and aPDCP layer 438 for communicating with PDCP layer 418 from the UE 410.

The eNB 430 further includes a protocol stack for communication with thesoftware gateway 450 over the S1-U interface. eNB 430 includes an L1440, a layer 2 (L2) 442, a universal datagram protocol (UDP)/IP layer444 and a global system for mobile communications (GSM) packet radioservice (GPRS) tunneling protocol user plane (GTP-U) layer 446.

Similarly SGW 450 includes an L1 452 for communicating with L1 440 ofeNB 430. SGW 450 further includes an L2 454, a UDP/IP layer 456 and aGTP-U layer 458.

SGW 450 further includes a protocol stack for communicating over theS5/S8 interface with the packet data network gateway (PGW) 470. Inparticular, SGW 450 includes an L1 layer 460, an L2 layer 462, an IPversion 4/version 6 (IPv4/v6) layer 464 and a tunnel layer 466.

PGW 470 includes an L1 472 for communicating with L1 460. PGW 470further includes an L2 474, an IPv4/v6 layer 476, and a tunnel layer478.

PGW 470 further includes an IP layer 480 which is used for communicationwith IP layer 420 of UE 410.

Thus FIG. 4 shows the protocol stack for an E-UTRAN.

Reference is now made to FIG. 5, which shows a protocol stack for aUTRAN. In particular UE 510 includes an L1 512, MAC layer 514, RLC layer516, PDCP layer 518, IP layer 520 and an application layer 522

Similarly, NodeB 530 includes an L1 532, a MAC layer 534, an RLC layer536 and PDCP layer 538, all of which are meant to communicate with UE510.

NodeB 530 further includes an L1 540, an L2 542, a UDP/IP layer 544 anda GTP-U layer 546, which are meant to communicate with a serving GPRSsupport node (SGSN) 550. In particular, SGSN 550 includes an L1 552, anL2 554, a UDP/IP layer 556 and a GTP-U layer 558 for communication withNodeB 530.

Similarly, SGSN 550 includes an L1 560, an L2 562, a UDP/IP layer 564and a GTP-U layer 566, all of which for communicating with the SGW 570.

SGW 570 includes an L1 572, an L2 574, a UDP/IP layer 576 and a GTP/Ulayer 578.

Similarly, SGW 570 includes an L1 580, an L2 582, an IPv4/v6, layer 584and a tunnel layer 586, which are meant to communicate with furthernetwork elements in the system.

From FIGS. 4 and 5 above, since the protocol stack at the servinggateway is the same for both the E-UTRAN and UTRAN and since the GTP-Uprotocol is common to both RATs, the same protocol stack can be used forthe multi-RAT X2 backhaul interface. This allows the same backhaulinterface to be used between different RATs (HSPA and LTE) as in thecase of the same RAT (X2 interface between eNBs).

Reference is now made to FIG. 6, which shows a protocol stack for thecontrol plane in accordance with one embodiment of the presentdisclosure.

In accordance with FIG. 6, a multi-RAT X2-U interface 610 and a NodeB612 utilizes four layers. In particular, eNB 610 has an L1 620, an L2622, a UDP-IP layer 624 and a GTP-U layer 626.

Similarly, NodeB 612 includes an L1 630, an L2 632, UDP-IP layer 634 anda GTP-U layer 636.

With regard to the user plane, reference is now made to FIG. 7. In FIG.7, eNB 710 communicates with NodeB 712. eNB 710 includes L1 720, L2 722,a stream control transmission protocol (SCTP) layer 724 and an X2application protocol (X2AP) layer 726.

Similarly, NodeB 712 includes a L1 730, L2 732, SCTP layer 734 and anX2AP layer 736.

In accordance with the above, when a multi-RAT transmission is enabled,a GTP tunnel is only established on the primary RAT. Since the multi-RATtransmission is transparent to the core network, no GTP tunnel isestablished on the secondary RAT. All packets to or from the corenetwork are sent to or from the node on the primary RAT. As used herein,the GTP tunnel is also referred to as an interface between the corenetwork and the primary RAT, and the interface includes both the controlplane and user plane.

On the radio access side, however, the UE receives packet on the primaryRAT as well as packets that have been forwarded to the secondary RAT bythe primary RAT through the multi-RAT backhaul.

Similarly, on the uplink, the UE may send packets on both the primaryand secondary RATs. In this case, the packets received by the networknode on the secondary RAT are forwarded to the network node on theprimary RAT for delivery to the upper layers of the primary RAT.

Reference is now made to FIG. 8, which shows an exemplary scenario wherethe E-UTRAN is the primary RAT and the UTRAN is the secondary RAT.

With reference to FIG. 8, UE 810 communicates with both UTRAN 812 andE-UTRAN 814.

Similarly, the E-UTRAN 814, in the embodiment of FIG. 8, communicateswith MME 816, as well as SGW 818. SGW 818 communicates with PDN-GW 820.

From UE 810, primary access is established with E-UTRAN 814, as shown byarrow 830. E-UTRAN 814 has a GTP tunnel between itself and SGW 818, asshown by arrow 832.

The GTP tunnel continues from SGW 818 to PDN-GW 820, as shown by arrow834.

UTRAN 812 and E-UTRAN 814 include the multi-RAT X2 interface betweenthem in the embodiment of FIG. 8, as shown by arrow 840 and therefore UE810 can have secondary access to the UTRAN 812, as shown by arrow 850.

In accordance with various embodiments, the interface between the RATsmay be either at the PDCP layer, the RLC layer, the MAC layer or the IPlayer. Each is described below.

PDCP Layer

In a multi-RAT transmission, the interface between two RATs may be atthe PDCP layer. This is the case for both the interface at the UE andbetween the network nodes over the multi-RAT X2.

In one embodiment, on the uplink, the UE may initiate an application onthe LTE RAT. The application packets are sent to the PDCP layer of theLTE RAT and some or all of the packets may be forwarded to the HSPA PDCPlayer over the multi-RAT PDCP interface at the UE. Packets flow throughboth protocol stacks and are then sent to their respective receivingnetwork nodes. At the PDCP layer of the receiving NodeB, the packets aresent to the LTE PDCP layer over the multi-RAT X2 interface. A similarpacket flow procedure may be used for downlink multi-RAT transmissions.

Reference is now made to FIG. 9, which shows a multi-RAT procedure andthe interface between the protocol stacks at the UE and between theUTRAN and E-UTRAN. In particular, UE 910 includes an LTE protocol stack912 and an HSPA protocol stack 914. In LTE protocol stack 912, the UE910 includes an LTE L1 layer 920, an LTE MAC layer 922, an LTE RC layer924, an LTE-PDCP layer 926, an IP layer 928 and an application layer929.

For the HSPA layer 914, the UE 910 includes an HSPA L1 930, an HSPA MAClayer 932, HSPA RLC layer 934 and an HSPA PDCP layer 936.

As will be appreciated by those in the art, the two protocol stacksdiffer with regard to the IP and application layers since the LTEnetwork is the primary RAT.

A UTRAN 940 includes a protocol stack for communicating with protocolstack 914 and in particular includes HSPA L1 942, HSPA MAC layer 944,HSPA RLC layer 946 and HSPA PDCP layer 948.

Similarly, an E-UTRAN 950 includes an LTE L1 layer 952, LTE MAC layer954, LTE RLC layer 956, and LTE PDCP layer 958. E-UTRAN 950 furtherincludes a protocol layer for communicating with the core network andincludes an L1 960, L2 962, UDP/IP layer 564 and GTP-U layer 966.

As seen in the embodiment of FIG. 9, the communication may be over thePDCP layer from LTE PDCP layer 926 either to LTE PDCP layer 958 directlythrough the E-UTRAN Uu interface 970. Alternatively, the LTE PDCP layer926 may communicate with HSPA PDCP layer 936 as shown by interface 972.HSPA PDCP layer 936 may then communicate with the HSPA PDCP layer 948 ofthe UTRAN 940 over a UTRAN Uu layer 974.

In the second case, the HSPA PDCP layer 948 communicates over themulti-RAT X2 backhaul 976 with LTE PDCP layer 958.

The multi-RAT communications at the PDCP layer requires changes at thePDCP layer itself. These are illustrated below with regard to FIG. 10.The example of FIG. 10 shows downlink communication for multi-RATtransmissions to a multi-RAT UE where LTE is the primary RAT and HSPA isthe secondary RAT. Figures for uplink transmissions, as well as for theHSPA being the primary RAT, are similar to those of FIG. 10.

In FIG. 10, application packets arrive at the PDCP layer of the LTE eNB,as shown by E-UTRAN 1010. The LTE PDCP layer assigns a sequence numberto the packets, as shown by block 1012. The header is then compressed atblock 1014. For service data unit (SDU) packets, the process proceeds toblock 1016, in which integrity protection is added and then cyphering isadded at block 1018. From block 1018, the process proceeds to block 1020in which the PDCP header is added. Similarly for non-SDU packets, fromblock 1014 the proceeds to block 1020.

Before sending the packet to a lower LTE layer, the packet passesthrough a RAT selection process, as shown by block 1022, where one orboth RATs may be selected to transmit the packet to the UE. If the LTERAT is selected, the packet is sent to the UE using existing LTEprocedures, as shown by arrow 1024.

Conversely, if either the HSPA RAT or both RATs are selected at block1022, then the packet is sent over the multi-RAT X2 interface to thePDCP layer of the UTRAN node 1030. In the case of a small cellheterogeneous network environment, in order to enable a “make beforebreak” handover, the PDCP PDU may be duplicated in one embodiment withthe identical content and sequencing number before it is sent to lowerLTE layers.

The HSPA PDCP layer selects the LTE packets and applies its ownmodifying PDCP functions with blocks 1032 and 1034. The modifications tothe PDCP layer include adding a multi-RAT header and adding logic toskip the header compression cyphering and integrity protection steps,since these are already performed by the LTE RAT. An HSPA PDCP layer isadded before sending the packet to the lower HSPA layers fortransmission to the UE, as shown by block 1036. The sending is over theUTRAN Uu interface, shown by arrow 1038.

At the receiving end, the UE receives the packet from both RATs or fromone of the RATs. At the HSPA PDCP layer, the UE first removes the HSPAPDCP header, as shown by block 1042. After applying the modified HSPAPDCP functions at block 1044, the packets are ordered, shown by block1046, and sent to the LTE PDCP layer over a multi-RAT PDCP interface atthe UE.

At the UE LTE PDCP layer, the PDCP layer header is removed, as shown byblock 1050 and deciphering and integrity verification occur at blocks1052 and 1054 respectively for SDU packets. Header decompression thenoccurs at block 1056. Non-SDU packets proceed directly from block 1050to 1056.

The packets are then ordered at block 1058 in accordance with thesequence number and can then be delivered to the LTE upper layers. Thereceiving side can select or combine the identical LTE PDCP PDUs if thePDCP PDUs are received from both the HSPA and LTE networks.

In one embodiment, if different packets from the same radio bearer aresent over different RATs then there may be an increase in the packetdelay if one of the RATs is slower. In order to limit the impact onpacket delay, a timer can be set for acknowledging the packets. If thetimer expires before the packet is acknowledged then the packet may besent on the other RAT. If there are large packet delays on one of theRATs then all of the packets may be sent over the better RAT in oneembodiment.

RLC Layer

In an alternative embodiment, the interface between the two RATs may beat the RLC layer. In this case, the RLC PDU from the primary RAT may beencapsulated and sent to the secondary RAT. A multi-RAT header may beattached to the RLC protocol data unit (PDU). When the packet isreceived by the RLC of the secondary RAT, the multi-RAT header may beremoved and the packet treated as an RLC SDU by the secondary RAT.Reference is now made to FIG. 11.

In FIG. 11, an IP packet 1110 is received from the application layer anda PDCP header is added at the LTE PDCP layer, as shown by referencenumeral 1120. The LTE RLC Layer converts the PDCP packet into an RLCSDU, as shown by reference numeral 1130 and an RLC header is added, asshown by reference numeral 1132.

The RLC SDU is then transported over the multi-RAT interface with aheader and an LTE RLC PDU as shown by block 1140. At the HSPA RLC layer,the RLC header and RLC SDU are created, as shown by blocks 1142 and1144.

The RLC header and RLC SDUs are converted to MAC SDUs at the HSPA MAClayer, as shown by block 1150 and a MAC header and padding are added atblock 1152.

The packet is then transported at the HSPA physical layer, shown byblock 1160.

Since the channel quality is likely to be different for different RATs,a different RLC PDU segment size may be selected by each RAT where thesegment size may fit within the total size of the RLC PDUs indicated bythe lower layer in a particular transmission opportunity. In this case,feedback from the primary RAT or the total size of the RLC PDU forparticular transmission opportunity may be available, for examplethrough the multi-RAT X2 interface, for proper RLC PDU segment sizesselection.

Alternatively, the multi-RAT backhaul interface may be between the PDCPlayer of the primary RAT and the RLC layer of the secondary RAT. Thismay reduce the complexity of performing the RLC layer functions in bothRATs.

MAC Layer

In an alternative, the interface between the two RATs may be at the MAClayer. In this case, the MAC PDU from the primary RAT may beencapsulated and sent to a secondary RAT. A multi-RAT header may beattached to the MAC PDU from the primary RAT. When the packet isreceived by the MAC layer of the secondary RAT, the multi-RAT header maybe removed and the packet treated as a MAC SDU by the secondary RAT.This is illustrated below with regard to FIG. 12.

In accordance with the embodiment of FIG. 12, an IP packet is receivedfrom an application layer on a multi-RAT UE and at the PDCP layer a PDCPheader is added, as shown by reference numeral 1220. The packet is thenprovided to the RLC layer which uses the PDCP header and the IP packetas the RLC SDU and adds an RLC header as shown by reference numeral1230.

The RLC header and RLC SDUs are provided to the MAC layer, which thentreats them as a MAC SDU and adds a MAC header and padding as shown byreference numeral 1240. The packet is then provided with a multi-RATheader and transported over the multi-RAT interface to the HSPA MAClayer.

At the HSPA MAC layer, the header is stripped and the HSPA MAC layertreats the packet as a MAC SDU. The secondary RAT then adds a MAC headerand padding, shown by block 1250, and sends the packet over the physicallayer transport layer as a transport block 1260.

IP Layer

In a fourth embodiment, the multi-RAT backhaul interface may be at theIP layer. In this case, IP packets are diverted to the secondary RAT andthe full radio protocol stack is enabled on both RATs. Another layer maybe inserted between the IP layer and the PDCP layer to handle the RATselection process.

The above is illustrated with regard to FIG. 13. In particular, in FIG.13 the IP packet is sent between a multi-RAT layer 1320 of E-UTRAN 1310and multi-RAT layer 1322 of UTRAN 1312. Protocol stacks, including theLTE PDCP layer 1330, the LTE RLC layer 1332 the LTE MAC layer 1335 andthe LTE L1 layer 1336 are used.

The communication can then be transmitted over the E-UTRAN Uu interface1338 to the LTE protocol stack on UE 1340. The LTE protocol stack on UE1340 includes LTE L1 layer 1342, LTE MAC layer 1344, LTE RLC layer 1346,and LTE PDCP layer 1348. The multi-RAT layer 1350, IP layer 1352 andapplication layer 1356 are then used for both HSPA and LTE.

Similarly, UTRAN 1312 includes a HSPA PDCP layer 1360, HSPA RLC layer1362, HSPA MAC layer 1364, and HSPA L1 layer 1366, and communication isthen sent over the UTRAN Uu interface 1368.

At the UE 1340, HSPA L1 layer 1370 forms the first part of the HSPAprotocol stack. Similarly HSPA MAC layer 1372, HSPA RLC layer 1374 andHSPA PDCP layer 1376 form the HSPA protocol stack before a multi-RATlayer 1350. Thus, the use of the IP adds the multi-RAT layer 1320 and1322 to the E-UTRAN 1310 and the UTRAN 1312, respectively.

With the above, each of the layers can be used where a header is addedfor the multi-RAT X2 interface which can then be stripped at the otherof the primary or the second RAT to form the packet at the appropriatelayer of the protocol stack. This approach may also be used to aggregateLTE with WiFi (e.g. IEEE 802.11n, 11ad, 11af). In this case, The LTE RATis the primary RAT and can decide when to offload some or all of thepackets to WiFi. The multi-RAT X2 interface may be between the WiFi MAClayer and the LTE IP, PDCP, RLC or MAC layer. A new RAT selection layermay be inserted below the LTE IP, PDCP or RLC layer to handle the RATselection process between LTE and WiFi. A similar multi-RAT interfacemay be implemented at the UE to forward the packets received from WiFito LTE. Feedback for the WiFi transmissions (e.g. ACK/NACK and CQI) maybe sent on the LTE UL and forwarded to the WiFi AP over the multi-RATX2. This may be used when there are coexistence issues in the case wherethe LTE carrier is adjacent to the band used by WiFi.

Handover

As the UE moves across network coverage areas of both the primary andthe secondary RATs, the UE may need to handover from one network node onthe primary RAT, the secondary RAT or both. Multi-RAT transmissions canbe used to reduce handover interruption times.

In a first embodiment, handover may occur on the primary RAT. If the UEmoves out of the coverage area of the network node on the primary RATand remains within the coverage area of the network node on thesecondary RAT, the UE may still receive packets from the secondary RATwhile undergoing handover on the primary RAT. This embodiment may occur,for example, where the primary RAT is a small cell LTE cell and thesecondary RAT is a much larger UMTS cell. If the UE receives a handovercommand on the primary RAT then the UE detaches from the old cell andsynchronizes with the new cell of the primary RAT. The primary RAT thentransfers the buffered and in transit packets to the target cell. If thetarget cell has enough resources to handle the UE's traffic withoutassistance from the secondary RAT then the buffered packets may beforwarded to the target cell of the primary RAT.

Otherwise, if the target cell of the primary RAT cannot support theadditional data flow, the target cell may establish a multi-RAT backhaulconnection with the network node of the secondary RAT. The sourceprimary RAT sends handover information to the target primary RAT so thatthe target primary RAT can determine if it is capable of handling thetraffic for the UE or if it needs assistance from the secondary RAT. Thehandover information may include information such as buffer size,traffic type and delay or quality of service constraints.

The packets that were sent to the secondary RAT node may be transmittedto the UE without any interruption since the UE maintains the connectionon the secondary RAT. Similarly, on the uplink, the UE may continue tosend data without any interruption.

Reference is now made to FIG. 14 which shows a UE 1410 communicatingwith a primary RAT 1412 and a secondary RAT 1414. The UE moves out ofthe coverage area of primary RAT 1412 and into coverage area of asecond, target primary RAT 1416.

Initially, UE 1410 includes a data connection 1420 with the sourceprimary RAT 1412 and the source primary RAT 1412 includes a multi-RAT X2interface with secondary RAT 1414, as shown by arrow 1422.

Data may then be exchanged between secondary RAT 1414 and UE 1410, asshown by arrow 1424.

Once the UE moves out of coverage of the primary RAT, as shown by block1426, the primary RAT 1412 makes a handover decision, shown by block1428.

The source primary RAT 1412 makes a handover request to target primaryRAT 1416, as shown by arrow 1430 and an acknowledgement is sent back tothe source primary RAT 1412, as shown by arrow 1432. The source primaryRAT 1412 then sends a handover command 1440 to UE 1410.

Once the handover command is received, the UE detaches from the sourceprimary RAT, as shown by block 1442.

While the UE is detaching, the source primary RAT 1412 sends handoverinformation to the secondary RAT 1414, as shown by arrow 1450. Thesource primary RAT 1412 further forwards data to the target primary RAT1416, as shown by arrow 1452.

If required, target primary RAT 1416 may establish a multi-RAT X2interface, as shown by arrow 1454.

The source primary RAT 1412 then can receive a handover complete commandfrom the target primary RAT 1416, as shown by arrow 1460 and detach themulti-RAT X2 interface, as shown as arrow 1462.

Thus, based on the above, during messages 1450 to 1462, the UE maycontinue to receive data from the secondary RAT.

The UE then performs a connection establishment with the target primaryRAT 1416, as shown by arrow 1470. Data can then be passed from targetprimary RAT 1416 to the secondary RAT 1414, as shown by arrow 1472 andthis data can then be transmitted to the UE 1410 from one or both of theRATs.

In one embodiment, if the handover is an S1-based handover, the primaryRAT may inform the secondary RAT to terminate the connection towards theUE before the actual S1 handover occurs.

In a second embodiment, if the UE moves out of the coverage area of thesecondary RAT, while still within the coverage area of the primary RAT,the UE may undergo a handover on the secondary RAT. The decision onwhether to handover the UE to another secondary RAT node depends onwhether or not the primary RAT node and target secondary RAT node canestablish a multi-RAT backhaul and the available resources on the targetsecondary RAT node.

The handover procedure of the secondary RAT is simplified compared tothat of the primary RAT since there is no path switch required at theMME and the serving gateway. Since the multi-RAT transmission istransparent to the core network, the MME and serving gateway are notaware of the handover on the secondary RAT.

In this case, the source network node of the secondary RAT makes ahandover decision based on the UEs neighbor cell measurements and basedon the availability of the target node of the secondary RAT.

If the target secondary RAT node has enough resources to admit the UEthen the multi-RAT transmission handover of the secondary RAT isillustrated in the signalling diagram in FIG. 15.

Referring to FIG. 15, a UE 1510 initially communicates with a primaryRAT 1512 and a source secondary RAT 1514. In accordance with theembodiment of FIG. 15, a target secondary RAT 1516 may be used forcommunication and the secondary RAT is transferred from the sourcesecondary RAT 1512 to target secondary RAT 1516.

In particular, UE 1510 includes a data connection with the primary RAT1512, as shown by arrow 1520 and a data connection with the sourcesecondary RAT 1514, as shown by arrow 1522. Further, a multi-RAT X2interface exists between primary RAT 1512 and source secondary RAT 1514,as shown by arrow 1524.

The UE moves out of the coverage area of the secondary RAT, as shown byblock 1526 and the source secondary RAT 1514 then makes a handoverdecision, as shown by block 1528. Based on measurement reports, thesource secondary RAT 1514 makes a handover request to target secondaryRAT 1516, as shown by arrow 1530. The handover request may includeinformation about primary RAT 1512 in one embodiment. An acknowledgementis received at arrow 1532.

The source secondary RAT 1514 provides handover information to theprimary RAT 1512, as shown by arrow 1534, and further sends a handovercommand to UE 1510, as shown by arrow 1536.

The secondary RAT 1514 provides data for the UE to the target secondaryRAT 1516, as shown by arrow 1540, and a multi-RAT X2 interface isestablished between the primary RAT 1512 and the target secondary RAT1516, as shown by arrow 1542.

The UE then detaches from the source secondary RAT 1514, as shown byblock 1550 and makes a connection establishment with the targetsecondary RAT 1516, as shown by arrow 1552. Between the handover atarrow 1536 and the connection establishment at arrow 1552, the UE cancontinue to receive data from the primary RAT.

Once the connection is established between UE 1510 and secondary RAT1516, data connections can be established between the target secondaryRAT 1516 and the primary RAT 1512, as shown by arrow 1560 and alsobetween the target secondary RAT 1516 and UE 1510, as shown by arrow1562.

Based on FIG. 15, the handover therefore occurs without the UE losingdata connectivity with the primary RAT.

In a third embodiment, the UE may move out of the coverage area of boththe primary and the secondary RAT simultaneously. This case may occurwhen the primary and the secondary nodes are co-located. In this case,the UE may first begin a handover procedure for the primary RAT, whilemaintaining a connection on the secondary RAT. During the handoverprocedure on the primary RAT, the primary RAT and the secondary RATexchange the multi-RAT handover information. This includes the targetnode of both RATs.

Once the handover information is exchanged, and if it is determined thatthe target node on the secondary RAT will assist transmission to the UE,the target nodes of both RATs may setup a multi-RAT backhaul for thespecified UE. When the setup is complete, the source node of thesecondary RAT sends a handover command to the UE.

After the UE synchronizes and establishes a connection with the targetnode of the secondary RAT, the target node of the secondary RAT informsthe target node of the primary RAT that the handover of the secondaryRAT is complete. Since the IP packets are only sent to the primary RAT,the handover on the secondary RAT is simplified. The remaining steps inthe handover procedure are performed by the nodes on the primary RAT.These steps include the path switch request and acknowledgement by theMME and serving gateway.

A signalling diagram for the handover of both the primary and thesecondary RATs is shown with regard to FIG. 16. Referring to FIG. 16, UE1610 communicates with both the primary RAT 1612 and the secondary RAT1614. Initially, a data connection is established between the primaryRAT and UE as well as the secondary RAT and the UE, as shown by arrows1620 and 1622. Further, a multi-RAT X2 interface is established betweenthe primary RAT 1612 and the secondary RAT 1614, as shown by arrow 1624.

The UE then moves out of the coverage of the primary and the secondaryRATs, as shown by block 1630 and the primary RAT 1612 makes a handoverdecision based on measurement reports to a target primary RAT 1616, asshown by block 1632.

The source primary RAT 1612 sends a handover request 1634 to the targetprimary RAT 1616 and an acknowledgement is sent back at arrow 1636. Atthis point, primary RAT 1612 forwards data to the target primary RAT1616, as shown by arrow 1638, as well as a handover command to the UE,as shown by arrow 1640.

After receiving the handover command, the UE detaches from the sourceprimary RAT as shown by block 1642 and provides a connectionestablishment, as shown by arrow 1644, with the target primary RAT 1616.

Target primary RAT 1616 then enables a secondary RAT handover decision,as shown by block 1650 and sends a measurement request to the UE 1610,as shown by arrow 1652. The measurement report is provided from the UEat arrow 1654 and based on the measurement report a multi-RAT X2interface is established with a secondary RAT 1618, as shown by arrow1660. A command is sent from the target primary RAT 1616 to UE 1610 tosynchronize with the target secondary RAT, as shown by arrow 1662 and atthat point a data connection may be established between the primary RAT1616 and the secondary RAT 1618, as shown by arrow 1664.

A connection establishment is performed between the UE and the targetsecondary RAT 1618, as shown by arrow 1670, at which point data canproceed either from the target primary RAT 1616 and the UE 1610 or thetarget secondary RAT 1618 and the UE 1610, as shown by arrows 1672 and1674 respectively.

In a fourth embodiment, a handover may occur from the primary RAT to thesecondary RAT. For example, it may be possible that the primary RAT isno longer available when the UE moves out of the coverage of the primaryRAT node. For example, if the primary RAT is an LTE hotspot, it may notbe available beyond the LTE small cell. Since there is no target primaryRAT, the entire session may be handed over to the secondary RAT. In thiscase, the secondary RAT then becomes the primary RAT with a fullconnection to the core network.

When the UE moves out of the coverage area of the primary RAT node andthe source primary RAT node makes the handover decision, it sends ahandover request message to the secondary RAT node. Since the UE isalready synchronized and communicating with the secondary RAT node, thismessage is to instruct the node to complete the handover. The secondaryRAT node will then become the primary RAT node.

The primary RAT node also sends a handover command to the UE to informit that the secondary RAT node will become the new primary RAT node andthat it can detach from the primary RAT node. The handover command mayinclude new encryption keys for communicating with the new target nodewhen the handover is completed. There may be an indication in thehandover command which specifies the secondary RAT becoming the newprimary RAT as the primary cell and the UE may start to monitor thecontrol channel such as the PDCCH in case of LTE from the new primaryRAT and sending the control channel such as the PUCCH in the case of LTEto the new primary RAT after handover.

The secondary RAT may send a path switch request to the MME and the MMEmay send an update user plane request to the serving gateway as in anormal handover. The secondary RAT continues to serve the UE frompackets forwarded on the multi-RAT backhaul until the path switch iscomplete. When the path switch is complete, the multi-RAT X2 can bedisabled for the UE.

An indication may also be provided in the path switch request thatspecifies that the secondary RAT becomes the new primary RAT as aprimary cell and that the MME will receive a non-access stratum (NAS)message to the UE, for example through a downlink information transfer.

Reference is now made to FIG. 17. In particular, UE 1710 is served by aprimary RAT 1712 and a secondary RAT 1714, and can receive data fromboth, as shown by arrows 1720 and 1722 respectively. A multi-RAT X2interface is established between primary RAT 1712 and secondary RAT1714, as shown by arrow 1724.

The UE moves out of the coverage range of the primary RAT 1712, as shownby block 1730 and thus the primary RAT 1712 makes a handover decision asshown by block 1732. A handover request is then made to the secondaryRAT 1714, as shown by arrow 1734, and a handover command is sent to UE1710, as shown by arrow 1736. The UE then detaches from the primarycell, as shown by block 1740.

When the handover request is made to the source secondary RAT 1714 thenthe secondary RAT 1714 makes a path switch request to MME 1716, as shownby arrow 1750 and a user plane update request is then made between MME1716 and SGW 1718, as shown by arrow 1752.

The SGW 1718 then switches the downlink path, as shown by block 1754 andsends an end marker to the primary RAT 1712, as shown by arrow 1756.

A data connection is then established between the secondary RAT 1714 andthe SWG 1718, shown by arrow 1760.

The primary RAT sends an end marker to the secondary RAT 1714, as shownby arrow 1762 and the multi-RAT X2 interface is disabled, as shown byarrow 1764.

SGW 1718 then sends a user plane update response to MME 1716, as shownby arrow 1770 and the path switch acknowledgement is sent from MME 1716to the secondary RAT 1714, as shown by arrow 1772. The secondary RAT1714 then sends a UE context release to the primary RAT 1712, as shownby arrow 1774 and then the primary RAT 1712 may release resources, shownby block 1776. Based on the above, secondary RAT 1714 becomes theprimary RAT.

The above may be implemented by any network element. A simplifiednetwork element is shown with regard to FIG. 18.

In FIG. 18, network element 1810 includes a processor 1820 and acommunications subsystem 1830, where the processor 1820 andcommunications subsystem 1830 cooperate to perform the methods describedabove.

Further, the above embodiments may be implemented by any UE. Oneexemplary device is described below with regard to FIG. 19.

UE 1900 is typically a two-way wireless communication device havingvoice and data communication capabilities. UE 1900 generally has thecapability to communicate with other computer systems on the Internet.Depending on the exact functionality provided, the UE may be referred toas a data messaging device, a two-way pager, a wireless e-mail device, acellular telephone with data messaging capabilities, a wireless Internetappliance, a wireless device, a mobile device, or a data communicationdevice, as examples.

Where UE 1900 is enabled for two-way communication, it may incorporate acommunication subsystem 1911, including both a receiver 1912 and atransmitter 1914, as well as associated components such as one or moreantenna elements 1916 and 1918, local oscillators (LOs) 1913, and aprocessing module such as a digital signal processor (DSP) 1920. As willbe apparent to those skilled in the field of communications, theparticular design of the communication subsystem 1911 will be dependentupon the communication network in which the device is intended tooperate. Further, communications subsystem 1911 may be capable ofcommunicating with multiple RATs, and have a plurality of antennas andother components in some embodiments.

Network access requirements will also vary depending upon the type ofnetwork 1919. In some networks network access is associated with asubscriber or user of UE 1900. A UE may require a removable useridentity module (RUIM) or a subscriber identity module (SIM) card. TheSIM/RUIM interface 1944 is normally similar to a card-slot into which aSIM/RUIM card can be inserted and ejected. The SIM/RUIM card can havememory and hold many key configurations 1951, and other information 1953such as identification, and subscriber related information.

When required network registration or activation procedures have beencompleted, UE 1900 may send and receive communication signals over thenetwork 1919. As illustrated in FIG. 19, network 1919 can consist ofmultiple base stations communicating with the UE. In one embodiment,network 1919 can comprise multiple RATs.

Signals received by antenna 1916 from communication network 1919 areinput to receiver 1912, which may perform such common receiver functionsas signal amplification, frequency down conversion, filtering, channelselection and the like. ND conversion of a received signal allows morecomplex communication functions such as demodulation and decoding to beperformed in the DSP 1920. In a similar manner, signals to betransmitted are processed, including modulation and encoding forexample, by DSP 1920 and input to transmitter 1914 for digital to analogconversion, frequency up conversion, filtering, amplification andtransmission over the communication network 1919 via antenna 1918. DSP1920 not only processes communication signals, but also provides forreceiver and transmitter control. For example, the gains applied tocommunication signals in receiver 1912 and transmitter 1914 may beadaptively controlled through automatic gain control algorithmsimplemented in DSP 1920.

UE 1900 generally includes a processor 1938 which controls the overalloperation of the device. Communication functions, including data andvoice communications, are performed through communication subsystem1911. Processor 1938 also interacts with further device subsystems suchas the display 1922, flash memory 1924, random access memory (RAM) 1926,auxiliary input/output (I/O) subsystems 628, serial port 630, one ormore keyboards or keypads 1932, speaker 1934, microphone 1936, othercommunication subsystem 1940 such as a short-range communicationssubsystem, WiFi communications subsystem, among others, and any otherdevice subsystems generally designated as 1942. Serial port 1930 couldinclude a USB port or other port known to those in the art.

Some of the subsystems shown in FIG. 19 perform communication-relatedfunctions, whereas other subsystems may provide “resident” or on-devicefunctions. Notably, some subsystems, such as keyboard 1932 and display1922, for example, may be used for both communication-related functions,such as entering a text message for transmission over a communicationnetwork, and device-resident functions such as a calculator or tasklist.

Operating system software used by the processor 1938 may be stored in apersistent store such as flash memory 1924, which may instead be aread-only memory (ROM) or similar storage element (not shown). Thoseskilled in the art will appreciate that the operating system, specificdevice applications, or parts thereof, may be temporarily loaded into avolatile memory such as RAM 1926. Received communication signals mayalso be stored in RAM 1926.

As shown, flash memory 1924 can be segregated into different areas forboth computer programs 1958 and program data storage 1950, 1952, 1954and 1956. These different storage types indicate that each program canallocate a portion of flash memory 1924 for their own data storagerequirements. Processor 1938, in addition to its operating systemfunctions, may enable execution of software applications on the UE. Apredetermined set of applications that control basic operations,including at least data and voice communication applications forexample, will normally be installed on UE 1900 during manufacturing.Other applications could be installed subsequently or dynamically.

Applications and software may be stored on any computer readable storagemedium. The computer readable storage medium may be a tangible or intransitory/non-transitory medium such as optical (e.g., CD, DVD, etc.),magnetic (e.g., tape) or other memory known in the art.

One software application may be a personal information manager (PIM)application having the ability to organize and manage data itemsrelating to the user of the UE such as, but not limited to, e-mail,calendar events, voice mails, appointments, and task items. Naturally,one or more memory stores would be available on the UE to facilitatestorage of PIM data items. Such PIM application may have the ability tosend and receive data items, via the wireless network 1919. Furtherapplications may also be loaded onto the UE 1900 through the network619, an auxiliary I/O subsystem 1928, serial port 1930, short-rangecommunications subsystem 1940 or any other suitable subsystem 1942, andinstalled by a user in the RAM 1926 or a non-volatile store (not shown)for execution by the processor 1938. Such flexibility in applicationinstallation increases the functionality of the device and may provideenhanced on-device functions, communication-related functions, or both.For example, secure communication applications may enable electroniccommerce functions and other such financial transactions to be performedusing the UE 1900.

In a data communication mode, a received signal such as a text messageor web page download will be processed by the communication subsystem1911 and input to the processor 1938, which may further process thereceived signal for output to the display 1922, or alternatively to anauxiliary I/O device 1928.

A user of UE 1900 may also compose data items such as email messages forexample, using the keyboard 1932, which may be a complete alphanumerickeyboard or telephone-type keypad, among others, in conjunction with thedisplay 1922 and possibly an auxiliary I/O device 1928. Such composeditems may then be transmitted over a communication network through thecommunication subsystem 1911.

For voice communications, overall operation of UE 1900 is similar,except that received signals would typically be output to a speaker 1934and signals for transmission would be generated by a microphone 1936.Alternative voice or audio I/O subsystems, such as a voice messagerecording subsystem, may also be implemented on UE 1900. Although voiceor audio signal output is generally accomplished primarily through thespeaker 1934, display 1922 may also be used to provide an indication ofthe identity of a calling party, the duration of a voice call, or othervoice call related information for example.

Serial port 1930 in FIG. 19 would normally be implemented in a personaldigital assistant (PDA)-type UE for which synchronization with a user'sdesktop computer (not shown) may be desirable, but is an optional devicecomponent. Such a port 1930 would enable a user to set preferencesthrough an external device or software application and would extend thecapabilities of UE 1900 by providing for information or softwaredownloads to UE 1900 other than through a wireless communicationnetwork. The alternate download path may for example be used to load anencryption key onto the device through a direct and thus reliable andtrusted connection to thereby enable secure device communication. Aswill be appreciated by those skilled in the art, serial port 1930 canfurther be used to connect the UE to a computer to act as a modem.

Other communications subsystems 1940, such as a short-rangecommunications subsystem, is a further optional component which mayprovide for communication between UE 1900 and different systems ordevices, which need not necessarily be similar devices. For example, thesubsystem 1940 may include an infrared device and associated circuitsand components or a Bluetooth™ communication module to provide forcommunication with similarly enabled systems and devices. Subsystem 1940may further include non-cellular communications such as WiFi or WiMAX,or near field communications, among others.

The embodiments described herein are examples of structures, systems ormethods having elements corresponding to elements of the techniques ofthis application. This written description may enable those skilled inthe art to make and use embodiments having alternative elements thatlikewise correspond to the elements of the techniques of thisapplication. The intended scope of the techniques of this applicationthus includes other structures, systems or methods that do not differfrom the techniques of this application as described herein, and furtherincludes other structures, systems or methods with insubstantialdifferences from the techniques of this application as described herein.

The invention claimed is:
 1. A method for multi-radio access technology(RAT) carrier aggregation in a mobile network having a user equipmentconnected to a first node and a second node, the first node operating afirst radio access technology and the second node operating a secondradio access technology, the method comprising: determining the userequipment's capability to handle multi-RAT carrier aggregation, thedetermining comprising receiving a message from the user equipmentindicating the user equipment is capable of multi-RAT carrieraggregation; establishing a backhaul interface between the first nodeand the second node; receiving, at the first node from a core network, apacket for the user equipment; determining, after the receiving, tooffload the packet to the second node, the determining being based on arequired bandwidth for the user equipment; sending a request from thefirst node to the user equipment for a measurement report of the secondnode by the user equipment; receiving, at the first node, themeasurement report from the user equipment; determining that a qualityof the measurement report is above a threshold; adapting, at the firstnode, the packet at the Packet Data Convergence Protocol (PDCP) layerfor transmission using the second radio access technology, the adaptingcomprising adding a multi-RAT header to the packet at the PDCP layer;forwarding the packet to the second node using the backhaul interface,for delivery to the user equipment; starting a timer; and when the timerexpires prior to receiving an acknowledgement for the packet, sendingthe packet to the user equipment from the first node using the firstradio access technology; wherein the first radio access technology isdifferent from the second radio access technology; and wherein multi-RATcarrier aggregation allows for concurrent utilization of radio resourceson multiple RATs.
 2. The method of claim 1, wherein the first nodeincludes an interface to the core network for the user equipment.
 3. Themethod of claim 2, further comprising: receiving, at the first node, anuplink packet from the second node over the backhaul interface, theuplink packet originating from the user equipment; and forwarding theuplink packet from the first node to the core network.
 4. The method ofclaim 1, wherein the second node includes a tunnel to the core networkfor the user equipment.
 5. The method of claim 1, wherein the userequipment is configured to use radio resources of the first nodeaggregated with radio resources of the second node.
 6. The method ofclaim 5, wherein the aggregated radio resources are uplink radioresources, or downlink radio resources, or both of uplink and downlinkradio resources.
 7. The method of claim 1, wherein the first radioaccess technology is Long Term Evolution (LTE) and the second radioaccess technology is High Speed Packet Access (HSPA).
 8. The method ofclaim 1, further comprising determining, at the first node, an amount ofavailable resources of the second node.
 9. The method of claim 1,wherein the backhaul interface is over any one of a medium accesscontrol (MAC) layer, a radio link control (RLC) layer, a packet dataconvergence protocol (PDCP) layer, or an internet protocol (IP) layer.10. The method of claim 1, further comprising, sending the packet to theuser equipment from the first node using a first radio access interface.11. A network node operating a first radio access technology (RAT) in anetwork allowing multi-RAT carrier aggregation, comprising: a processor;and a communications subsystem; wherein the processor and thecommunications subsystem cooperate to: establish a backhaul interfacewith a second node, the second node operating a second radio accesstechnology distinct from the first radio access technology; receive,from a core network, a packet for a user equipment, the user equipmentbeing connected to the network node and the second node; determine, whenthe user equipment is connected to the network node and the second node,a capability of the user equipment to handle multi-RAT carrieraggregation, the determining comprising receiving a message from theuser equipment indicating the user equipment is capable of multi-RATcarrier aggregation; determine, after receiving the packet and accordingto the user equipment capability to handle multi-RAT carrieraggregation, to offload the packet to the second node, the determiningbeing based on a required bandwidth for the user equipment; send arequest to the user equipment for a measurement report of the secondnode by the user equipment; receive the measurement report from the userequipment; determine that a quality of the measurement report is above athreshold; adapting the packet at the Packet Data Convergence Protocol(PDCP) layer for transmission using the second radio access technology,the adapting comprising adding a multi-RAT header to the packet at thePDCP layer; forward the packet to the second node using the backhaulinterface, for delivery to the user equipment; start a timer; and whenthe timer expires prior to receiving an acknowledgement for the packet,send the packet to the user equipment from the first node using thefirst radio access technology; wherein multi-RAT carrier aggregationallows for concurrent utilization of radio resources on multiple RATs.12. The network node of claim 11, further including an interface to thecore network for the user equipment.
 13. The network node of claim 12wherein the processor and the communications subsystem are furtherconfigured to: receive an uplink packet from the second node over thebackhaul interface, the uplink packet originating from the userequipment; and forward the uplink packet to the core network.
 14. Thenetwork node of claim 11, wherein the user equipment is configured touse radio resources of the first node aggregated with radio resources ofthe second node.
 15. The network node of claim 14, wherein theaggregated radio resources are uplink radio resources, or downlink radioresources, or both of uplink and downlink radio resources.
 16. Thenetwork node of claim 11, wherein the first radio access technology isLong Term Evolution (LTE) and the second radio access technology is HighSpeed Packet Access (HSPA).
 17. The network node of claim 11, whereinthe processor and the communications subsystem are further configured todetermine an amount of available resources of the second node.
 18. Thenetwork node of claim 11, wherein the backhaul interface is over any oneof a medium access control (MAC) layer, a radio link control (RLC)layer, a packet data convergence protocol (PDCP) layer, or an internetprotocol (IP) layer.
 19. The network node of claim 11, wherein theprocessor and the communications subsystem are further configured tosend the packet to the user equipment using a first radio accessinterface.